Permanent magnet alloy using molybdenum

ABSTRACT

A semihard permanent magnet alloy characterized by relatively high coercive force, relatively high residual induction, high ductility and low magnetostriction and consisting essentially of cobalt, iron and molybdenum. The molybdenum content of this alloy, as expressed in percent by weight, falls within the approximate range 2 percent - 15 percent. The sum of the cobalt and iron falls within the approximate range 85 percent - 98 percent. The ratio by weight of cobalt to iron falls within the approximate range 6.5:1 to 7.5:1.

United States Patent Steinitz Robert PERMANENT MAGNET ALLOY USING MOLYBDENUM [75] Inventor: Robert Stei niti, Montclair, N1

[73] Assignee: Wilbur B. Driver Company,

Newark, NJ.

[22] Filed: Feb. 8, 1972 [21] Appl. No.: 224,613

Related US. Application Data [63] Continuation of Ser. No. 82,501, Oct. 20, 1970,

abandoned.

[52] US. Cl. 75/170, 148/3157 [51] Int. Cl. C22c 19/00' [58] Field of Search 75/170; 148/3155, 148/3157 56] References Cited UNITED STATES PATENTS 3,390,443 7/l968 Gould et a1. 148/3157 Jan. 15, 1974 1,927,940 9/1933 Koster ..14s/31.57 1,338,134 4/1920 Honda....., ..148/31.57

Primary Examiner-Richard 0. Dean Att0meyNorman J. OMalley et a1.

[57] ABSTRACT A semihard permanent magnet alloy characterized by relatively high coercive force, relatively high residual induction, high ductility and low magnetostriction and consisting essentially of cobalt, iron and molybdenum. The molybdenum content of this alloy, as expressed in percent by weight, falls within the approximate range 2 percent 15 percent. The sum of the cobalt and iron falls within the approximate range 85 percent 98 percent. The ratio by weight of cobalt to iron falls within the approximate range 6.5:1 to 7.5: l.

4 Claims, No Drawings PERMANENT MAGNET ALLOY USING MOLYBDENUM DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In forming my alloys, a thorough homogenization at CROSS'REFERENCE To RELATED APPLICATION 5 about 2,lF is required for all compositions. All al- This application is a continuation of Ser. No. 82,501 filed Oct. 20, l970, now abandoned and assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION Many types of electronic components and subsystems require the use of semihard permanent magnet alloys characterized by relatively high coercive force, low magnetostriction, high ductility and relatively high residual induction. Special alloys have been developed for this purpose. Such known alloys consist primarily of cobalt and iron, the ratio by weight of cobalt to iron being approximately seven, together with a third metal.

Insofar as I am aware the third metal can be gold (4 percent 6 percent), beryllium (1 percentpercent) niobium (3 percent 4 percent) or titanium (2 percent 8 percent).

Alloys incorporating each of the above-identified third metal have certain disadvantages. Gold, for example is not only very expensive, but results in a magnet alloy which is very difficult to homogenize, hot work or heat treat/Beryllium requires special precautions because it is a severe health hazard, and, moreover, it oxidizes readily, whereby the magnetic alloys, which should be oxide free, are not easily obtained. The maximum obtainable coercive force of the above alloys as well as the niobium containing alloys is too low for many applications. Finally, the use of titanium results in alloys having relatively low residual induction.

1 have developed a new semihard permanent magnetic alloy which overcomes these disadvantages. In particular my alloy employs a cobalt-iron matrix as in known alloys. but employs molybdenum as a third metal. The oxide of molybdenum is volatile whereby the resultant alloy is clean and contains no oxide inclusions. Further, molybdenum is easy to process and is a standard alloying addition for ferrous alloys; as a result, the alloy can be easily processed. Finally, the molybdenum containing alloys exhibit relatively high coercive force, high ductility and relatively high residual induction.

SUMMARY OF THE INVENTION In accordance with my invention, my alloy consists essentially of 2 percent percent by weight of molybdenum, balance cobalt and iron, the ratio of cobalt to iron falling with the range 6.5:l to 7.521. [This ratio is required to maintain very low magnetostriction and, thus, very low stress-sensitivity of the magnetic properties] In forming the alloy, the molybdenum goes into solution into the matrix of cobalt and iron at high temperature and precipitates during the aging heat treatment as grains of intermetallic compounds, thereby increasing substantially the coercive force. The alloy is highly ductile and can be drawn readily into fine wire. The relatively high coercive force can range upward over 70 Orst. Moreover the alloy exhibits relatively high residual induction which ranges upward over l4000 Gauss.

loys have to be cold worked, at least to between percent percent and, preferably, between 95 percent 99 percent. The higher the degree of cold work, the faster the molybdenum will precipitate in the cobaltiron matrix, whereby lower temperatures and shorter time periods can be employed in further processing. Optimal heat treatment depends upon the desired magnetic properties; to some degree, temperature and time can be interchanged.

Further information will be found in the specific examples which follow:

EXAMPLE I An alloy homogenized and cold worked as described above was found to have the following composition:

cobalt 85.5 percent iron 11.5 percent molybdenum 3. percent The alloy was drawn into wire of 0.04 inch in diameter and heat treated at a temperature of l,200F for a period of 2 hours. Measurements showed that the coercive force was 18 Orst; the residual induction was 14,400 Gauss; and the squareness ratio of the hysteresis curve was 0.92.

EXAMPLE II An alloy was produced having the following composition:

cobalt 83.5 percent iron l 1.5 percent molybdenum 5. percent This alloy was processed and tested as in Example I. The coercive force was 30 Orst; the residual induction was 13,000 Gauss; and the squareness ratio remained at 0.92.

EXAMPLE [II An alloy was produced having the following composition:

cobalt 8l percent iron 11 percent molybdenum 8 percent The alloy was processed and tested as in Example I. The coercive force was 72 Orst; the residual induction was 10,800 Gauss; and the squareness ratio was 0.85.

When the molybdenum content of my alloy was decreased appreciably below 2 percent, the amount of molybdenum precipitating during heat treatment was insufficient to produce the desired increase in coercive force. Conversely, when the molybdenum content of my alloy was increased appreciably above 15 percent, the entire amount of molybdenum did not go into solution, and the resulting structure did not exhibit the desired magnetic characteristics.

What is claimed is:

I. A semihard permanent magnet alloy consisting essentially of cobalt, iron and molybdenum wherein said molybdenum is from about 2 to about 15 percent by weight, the sum of cobalt and iron is from about 85 percent to about 98 percent by weight in a weight ratio of from about 6.5:1 to about 7.521 respectively.

2. An alloy according to claim 1 having g the followiron l 1.5 percent ing composition in percent by weight: molybdenum 5. percent cobalt 85.5 percent 4. An alloy according to claim 1 having the following iron 11.5 percent composition in percent by weight: molybdenum 3. percent 5 cobalt 81 percent 3. An alloy according to claim 1 having the following iron l 1 percent composition in percent by weight: molybdenum 8 percent cobalt- 83.5 percent 

2. An alloy according to claim 1 having g the following composition in percent by weight: cobalt - 85.5 percent iron - 11.5 percent molybdenum -
 3. percent
 3. An alloy according to claim 1 having the following composition in percent by weight: cobalt - 83.5 percent iron - 11.5 percent molybdenum -
 5. percent
 4. An alloy according to claim 1 having the following composition in percent by weight: cobalt - 81 percent iron - 11 percent molybdenum - 8 percent 